The sound card is what handles the computer's sound. It has its own processor. When you hear music coming from your computer's speakers, the sound card's processor is at work along with its digital-to-analog converter, processing and changing digital information into analog information that can be played through the speakers. When you talk into your computer's microphone, the sound card's processor is working along with its analog-to-digital converter to process and change the analog information received from the microphone into digital information. Better sound cards have better sound.